1. Field of the Invention
The present invention relates to a water based ink set for ink-jet recording and to an ink-jet recording method.
2. Description of the Related Art
An ink-jet recording system has been widely used for color-printing digital color image data. In order to achieve vivid color reproducibility, a water based ink set for ink-jet recording has been employed as ink-jet inks. The water based ink set comprises a magenta ink, a yellow ink and a cyan ink which are each prepared by dissolving a water soluble dye into a mixed solvent of water and water soluble organic solvents. In some cases, in order to print text data such as alphabet character data and Chinese character data, a dye based black ink is added to the water based ink set for ink-jet recording.
Recently, sharp text print quality has been desired in which blurring such as feathering is suppressed as much as possible. Additionally, a print quality close to photo image quality has been desired in which vivid color reproducibility and excellent lightfastness are implemented. However, if water soluble dyes are employed as coloring agents for all the inks of a water based ink set for ink-jet recording, feathering in text is unfavorably noticeable.
In order to implement sharp text, Japanese Patent Application Laid-Open No. 2001-354886 discloses an ink set for ink-jet recording comprising, in addition to the three primary color inks (yellow, magenta and cyan inks), three additional color inks (black, red and green inks), all of which are composed of pigment based inks.
If all of the inks of the ink set are composed of pigment based inks, the ink-jet image exhibits excellent lightfastness and excellent sharpness of text. However, although the additional black, red and green inks are employed together, the color reproducibility of the ink-jet image is not satisfactory as compared to that of the ink-jet image obtained by use of an ink set composed of dye based inks employing water soluble dyes. In addition, the number of nozzles of an ink-jet head must be increased, resulting in the problem of cost increase.
Thus, as an ink configuration which implements both sharp text print quality and vivid color reproducibility close to photo quality, a water based ink set for ink-jet recording has been commercially available which employs a pigment as a coloring agent for a black ink in which the print quality of text is of importance, and employs water soluble dyes as coloring agents for the color inks (e.g., yellow ink, magenta ink and cyan ink) in which color reproducibility is of importance.
However, when text data is printed by use of the water based ink set for ink-jet recording having the above-described ink configuration, red color, which is the second most frequently used color next to black color, is expressed by superposing the dye based yellow ink and the dye based magenta ink which both contain water soluble dyes. Therefore, feathering caused by a landing error of the superposition is noticeable. In addition, the degree of the feathering of the red color printed by use of the inks each employing the water soluble dye as the coloring agent is different from that of the black color printed by use of the pigment ink. Moreover, the water resistance and the lightfastness of the red color are worse than those of the black color. With respect to the water resistance, for example, blurring of a text document printed in an office is likely to occur due to sweat of a human hand or water such as a water drop from a drink, and also migration (blurring caused by moisture) tends to occur. With respect to the lightfastness, the fading of the red color caused by exposure to illumination light or sunlight becomes noticeable in a text document posted for a long period of time, and thus the letters become hard to read. A red color is often used for correction and letters to be emphasized, since it is more visually prominent than the other colors, and thus a print quality equivalent to that of the black color is required for a red color. However, under the present circumstances, since a red color is expressed by superposing a yellow ink and a magenta ink each employing a water soluble dye as a coloring agent, the print quality of the red color is significantly different from that of the black color expressed by a black ink employing a pigment as a coloring agent.